Tab key not editing text
One of the drawbacks of using "template" files created by someone else is that you have no control over them. Whatever choices the creator made are now part of the file.

The text in question is not editable as text anymore because it has been converted to a mesh. There is no operation to turn a mesh back to text.

You would need to create a new text object that fits your needs, and then copy or link to it whatever other attributes or animation the original mesh was using.

Something to be asked in a different question.